Method of introducing three streams of air into a combustor with selective heating

ABSTRACT

New combustors, and methods of operating same, which produce lower emissions, particularly lower emissions of nitrogen oxides. Methods and means are provided for supplying separate streams of air to primary and secondary combustion zones of a combustor, for removing heat from said primary combustion zone, and reintroducing said heat into the combustor at a region spaced apart and downstream from said primary and secondary combustion zones.

United States Patent [191 Quigg et al.

[ July 30, 1974 METHOD OF INTRODUCING THREE STREAMS OF AIR INTO ACOMBUSTOR WITH SELECTIVE HEATING Inventors: Harold T. Quigg; Robert M.

Schirmer, both of Bartlesville, Okla.

Assignee: Phillips Petroleum Company, Bartlesville, Okla.

Filed: Mar. 27, 1972 Appl. N0.: 238,317

Related US. Application Data Continuation-impart of Scr. No. 208,102,Dec. 15, 1971, abandoned.

US. Cl 60/39.02, 60/3906, 60/3951 R,

Int. Cl. F02c 1/00 Field of Search 60/3902, 39.06, 39.51, 60/3965,39.69; 431/10 References Cited UNITED STATES PATENTS l/l97l Vickers60/39.5l

FUEL

OTHER PUBLICATIONS Engineering Know-How in Engine Design, part 19 SAESP365 Hs-010922 pg. 7.

Primary Examiner-Carlton R. Croyle Assistant Examiner--Warren Olsen Newcombustors, and methods of operating same, which produce loweremissions, particularly lower emissions of nitrogen oxides. Methods andmeans are provided for supplying separate streams of air toprimary andsecondary combustion zones of a combustor, for removing heat from saidprimary combustion zone, and reintroducing said heat into the combustorat a region spaced apart and downstream from said primary and secondarycombustion zones.

ABSTRACT 19 Claims, 17 Drawing Figures pAlimwJuLsolsm SHEEI 2 OF 7 FIG.4

PATENTEDJULBOIBH SHEUHIF 7 2 7 K \\\1lli i Jo m METHOD OF INTRODUCINGTHREE STREAMS OF AIR INTO A COMBUST OR WITH SELE CTIVE HEATING Thisapplication is a continuation-in-part of copending application Ser. No.208,102, filed Dec. I5, 1971 now abandoned.

This invention relates to improved combustors and methods of operatingsame.

Air pollution has become a major problem in the United States and otherhighly industrialized countries of the world. Consequently, the controland/ or reduction of said pollution has become the object of majorresearch and development effort by both governmental and nongovernmentalagencies. Combustion of fossil fuel is a primary source of saidpollution. It has been alleged, and there is supporting evidence, thatautomobiles employing conventional piston-type engines burninghydrocarbon fuels are a major contricutor to said .pollution. Vehicleemission standards have been set by the United States EnvironmentalProtection Agency which are sufficiently restrictive to cause .3!E.Q. Qbj ma ia aqw er 9 c r. 9932192915 alternate engines instead of theconventional piston engme.

The gas turbine engine is being given serious consideration as analternate engine. However, insofar as we presently know, there is nopublished information disclosing realistic and/or practical combustorswhich can be operated at conditions typical of those existing in highperformance engines, and which will have emission levels meeting orreasonably approaching the standards set by said United StatesEnvironmental Protection Agency. This is particularly true with respectto nitrogen oxides emissions.

Thus, there is a need for a combustor of practical and/or realisticdesign which can be operated in a manner such that the emissionstherefrom will meet said standards. Even a combustor giving reducedemissions approaching siad standards would be a great advance in theart. Such a combustor would have great potential value because it ispossible the presently very restrictive standards may be reduced.

The present invention solves the above-described problems by providingimproved combustors, and methods of operating same, which produceemissions meeting or reasonably approaching the present strignentstandards established by said environmental protection agencies. Saidmethods comprise preferably supplying separate streams of air to primaryand secondary combustion zones of a combustor, removing heat from saidprimary combustion zone, and reintroducing said heat into the combustorat a region spaced apart from and downstream from said primary andsecondary zones.

Thus, according to the invention, there is provided a combustor,comprising, in combination: an outer casing; a flame tube disposedconcentrically within said casing and spaced apart therefrom to form afirst annular chamber between said flame tube and said casing; air inletmeans for introducing a first stream of air into the upstream endportion of said flame tube; fuel inlet means for introducing a fuel intothe upstream end portion of said flame tube; at least one openingprovided in the wall of said flame tube at a first station locatedintermediate the upstream and downstream ends thereof; an imperforateconduct means extending second stream of air into the interior of saidflame tube;

and at least one other opening provided in the wall of said flame tubeat a second station located downstream from said first station foradmitting a third stream of air from said first annular chamber into theinterior of said flame tube.

Further, according to the invention, there is provided a method forburning a fuel in a combustor, which method comprises: introducing afirst stream of air into a primary combustion zone of said combustor;introducing a fuel into said primary combustion zone; burning said fuel;introducing a second stream of air, separate from said first stream ofair, into a second zone of said combustor'located downstream from saidprimary combustion zone; passing a third stream of air, separate fromsaid first and second streams of air, in heat exchange with an outerwall of said primary combustion zone so as to remove heat from theinterior of said primary combustion zone and heat said air; andintroducing said thus-heated third stream of air into a third zone ofsaid combustor located downstream from said second zone.

FIG. 1 is a view, partially in cross section, of a combustor inaccordance with the invention.

FIGS. 2, 3, and 4 are cross section views taken along the line 2-2, 33,and 4-4, respectively, of FIG. 1.

FIG. 5 is a fragmentary perspective view of a combustor flame tubeillustrating another type of fin or extended surface which can beemployed therein.

FIG. 6 is a cross section view taken along the line 6-6 of FIG. 1.

FIG. 7 is a partial view in cross section of another combustor inaccordance with the invention.

FIG. 8 is a view in cross section taken along the line 8-8 of FIG. 7.

FIG. 9 is a partial view in cross section of another combustor inaccordance with the invention.

FIGS. 10 and 11 are cross section views taken along the lines 10-10 and11-11, respectively, of FIG. 9.

FIG. 12 is a view in cross section of another type of dome or closuremember which can be employed in the combustors of the invention.

FIGS. 13 and 14 are diagrammatic views, partially in cross section, ofother combustors in accordance with the invention.

FIG. 15 is a partial view in cross section of another combustor inaccordance with the invention.

FIG. 16 is a front elevation view taken along the line 16-16 of FIG. 15.

FIG. 17 is a cross-sectional elevation view of the swirl plate of thedome or closure member in the combustor of FIG. 15.

Referring now to the drawings, wherein like reference numerals areemployed to denote like elements, the invention will be more fullyexplained. In FIG. 1 there is illustrated a combustor in accordance withthe invention, denoted generally by the reference numeral 10, whichcomprises an elongated flame tube 12. Said flame tube 12 is open at itsdown stream end, as shown, for communication with a conduit leading to aturbine or other utilization of the combustion gases. A closure or domemember, designated generally by the reference numeral 14, is providedfor closing the upstream end of said flame tube, except for the openingsin said dome member. An outer housing or casing 16 is disposedconcentrically around said flanie tube 12 and spaced apart therefrom toform a first annular chamber 18 around said flame tube and said dome orclosure member 14. Said annular chamber 18 is closed at its downstreamend by any suitable means such as that illustrated. Suitable flangemembers, as illustrated, are provided at the downstream end of saidflame tube 12 and outer housing 16 for mounting same and connecting sameto a conduit leading to a turbine or other utilization of the combustiongases from the combustor. Similarly, suitable flange members and 17 areprovided at the upstream end of said flame tube 12 and said outerhousing 16 for mounting same and connecting same to a suitable conduitmeans which leads from a compressor or other source of air. Asillustrated in the drawing, said upstream flange members comprise aportion of said outer housing or casing 16 which encloses dome member 14and forms the upstream end portion of said first annular chamber 18. Itwill be understood that outer housing or casing 16 can be extended, ifdesired, to enclose dome 14 and said upstream flanges then relocated onthe upstream end thereof. While not shown in the drawing, it will beunderstood that suitable support members are employed for supportingsaid flame tube 12 and said closure member 14 in the outer housing 16and said flange members. Said supporting members have been omitted so asto simplify the drawing.

An air inlet means is provided for introducing a swirling mass or streamof air into the upstream end portion of flame tube 12. As illustrated inFIGS. 1 and 4, said air inlet means comprises a generally cylindricalswirl chamber 22 formed in said dome member 14. The downstream end ofswirl chamber 22 is in open communication with the upstream end of flametube 12. A plurality of air conduits 24 extend from said first annularchamber 18, or other suitable source of air, into swirl chamber 22tangentially with respect to the inner wall thereof.

A fuel inlet means is provided for introducing a stream of fuel into theupstream end portion of flame tube 12. As illustrated in FIG. 1, saidfuel inlet means comprises a hollow conduit 26 for introducing a streamof fuel into the upstream end of swirl chamber 22 and axially withrespect to said swirling stream of air. Any other suitable fuel inletmeans can be employed.

A flared expansion passageway 28 is formed in the downstream end portionof dome or closure member 14. Said flared passageway flares outwardlyfrom the o wjadmrfiqn QfJl IUQ 9r osurqmam s the inner wall of flametube 12.

An imperforate sleeve 30 surrounds an upstream portion of said flametube 12. The outer wall of said sleeve 30 can be insulated if desiredand thus increase its effectiveness as a heat shield. Said sleeve 30 isspaced apart from flame tube 12 so as to longitudinally enclose anupstream portion 18 of said first annular chamber 18 and define a secondannular chamber 19 between said sleeve 30 and outer casing 16. Anannular wall member 32, secured to the inner periphery of casing 16, isprovided for closing the downstream end of said second annular chamber19. At least one opening 34 is provided in the wall of flame tube 12 ata first station located intermediate the ends of said flame tube. Inmost instances, it will be preferred to provide a plurality of openings34, as illustrated. A generally tubular conduit means 36 extends fromsaid second annular chamber 19 into communication with said opening 34for admitting a second stream of air from said second annular chamber 19into the interior of flame tube 12. When a plurality of openings 34 areprovided, a plurality of said tubular conduits 36 are also provided,with each individual conduit 36 being individually connected to anindividual opening 34. The above described structure thus provides animperforate conduit means comprising second annular chamber 19 andtubular conduit(s) 36 for admitting a second stream of air into theinterior of flame tube 12.

At least one other opening 38 is provided in the wall of flame tube 12at a second station located downstream and spaced apart from said firststation for admitting a third stream of air from first annular chamber18 into the interior of flame tube 12. In most instances, it will bepreferred to provide a plurality of openings 38 spaced around theperiphery of said flame tube, similarly as illustrated.

Preferably, the outer wall surface of flame tube 12 is provided with anextended surface in the form of fins or tabs mounted thereon in theregion surrounded by sleeve 30, and which extend into the portion 18 ofsaid first annular chamber which is enclosed by said sleeve. Asillustrated in FIGS. 1, 2, and 3 said fins or tabs 40 and 42 can bearranged in rows which extend around the periphery of the flame tube 12,and which are spaced apart longitudinally on said flame tube..The finsor tabs 40, in each row thereof, can be spaced apart circumferentiallyto provide passageways 41 therebetween. See FIG. 2. Similarly,passageways 43 can be provided between the circumferentially spacedapart fins or tabs 42. See FIG. 3. FIG. 5 illustrates another type offin which can be employed. In FIG. 5 the fins 44 extend longitudinallyof flame tube 12. Said fins 40, 42, and 44 can extend into enclosedportion 18' any desired distance.

FIG. 6 illustrates one type of structure which can be employed toprovide tubular conduits 36. A plurality of boss members 37, spacedapart circumferentially in a row around the periphery of flame tube 12,is provided downstream from the last row of fins 42. Said boss members37 have the general shape of fins 40 and 42 and passageways 45 areprovided therebetween, similarly as for passageways 41 and 43 in therows of fins 40 and 42. Said imperforate sleeve 30 extends over bossmembers 37, similarly as for fins 40 and 42, and said conduits 36 can beformed by cutting through said sleeve 30 and said boss members 37 intocommunication with openings 34 in flame tube 12. Said passageways 41,43, and 45 thus provide communication from the upstream end of firstannular chamber 18, through enclosed portion 18, around tubular conduits36, and into the downstream portion of first annular chamber 18.

Referring now to FIG. 7, there is illustrated the upstream portion ofanother combustor in accordance with the invention. The downstreamportion not shown is like the combustor of FIG. 1. In FIG. 7, a closureor dome member, designated generally by the reference numeral 46, isprovided for closing the upstream end of flame tube 12, except for theopenings in said dome member. Said dome member can be fabricatedintegrally, i.e., as one element. However, in most instances it will bepreferred to fabricate said closure member 46 as two or more elements,e.g., an upstream element 48 and a downstream element 50.'A generallycylindrical swirl chamber 52 is formed in said upstream element 48 ofclosure member 46. The downstream end of said swirl chamber 52 is inopen communication with the upstream end of said flame tube 12. An airinlet means is provided for introducing a swirling mass of air into theupstream end portion of said swirl chamber 52 and then into the upstreamend of said flame tube. As illustrated in FIGS. 7 and 8, said air inletmeans comprises a plurality of air conduits 54 extending into said swirlchamber 52 tangentially with respect to the inner wall thereof. Saidconduits 54 extend from first annular passageway or chamber 18 into saidswirl chamber 52.

A fuel inlet means is provided for introducing a stream of fuel in adirection which is from tangent to less than perpendicular, butnonparallel, to the periphery of said stream of air. As illustrated inFIGS. 7 and 8, said fuel inlet means comprises a fuel conduit '56leading from a source of fuel, commujnicating with a passageway 58,which in turn communicates with fuel passageway 60 which is formed by aninner wall of said downstream element 50 of closure member 46 and thedownstream end wall of said upstream element 48 of closure member 46. Itwill be noted that the inner wall of said downstream element is spacedapart from and is complementary in shape to the downstream end wall ofsaid upstream element 48. The direction of the exit portion of said fuelpassageway 60 can be varied over a range which is intermediate orbetween tangent and perpendicular, but nonparallel, to the periphery ofthe stream of air exiting from swirl chamber 52. Varying the directionof the exit portion of fuel passageway 60 provides one means or methodfor controlling the degree of mixing between the fuel stream and saidair stream at the interface therebetween. As illustrated in FIG. 7, thedirection of the exit portion of fuel passageway 60 is at an angle ofapproximately 45 degrees with respect to the periphery of the airexiting from swirl chamber 52. As mentioned above, the direction of saidexit portion can vary from between tangent and perpendicular, butnonparallel, to the periphery of the stream of air from swirl chamber26. Generally speaking, in most instances, it will be deisred that theexit portion of said fuel passageway 60 have a direction which forms anangle within the range of from about to about 75, preferably about 30 toabout 60, with respect to the periphery of the stream of air exitingfrom swirl chamber 52. In most instances, it will be preferred that thefuel from fuel passageway 60 be introduced in a generally downstreamdirection. However, it is within the scope of the invention to introducesaid fuel in an upstream direction. Shim 62 provides means for varyingthe width of said fuel passageway 60. Any other suitable means, such astheads provided on the wall of upstream element 48 and downstreamelement 50, can be provided for varying the width of said fuelpassageway 60. As will be understood by those skilled in the art in viewof this disclosure, the shape of the upstream inner wall of saiddownstream element 50 and the shape of the downstream end wall of saidupstream element 48 can be changed, but maintained complementary withrespect to each other, so as to accommodate the above-described changesin direction and width of said fuel passageway 60.

Referring now to FIG. 9, there is illustrated the upstream portion ofanother combustor in accordance with the invention. The downstreamportion of the combustor of FIG. 9 is like the combustor of FIG. 1. Aclosure member 64 is mounted in the upstream end of flame tube 12 in anysuitable manner so as to close the upstream end of said flame tubeexcept for the openings provided in said closure member. A generallycylindrical swirl chamber 66 is formed in said closure member 64. Thedownstream end of said swirl chamber is in open communication with theupstream end of said flame tube. An air inlet means is provided forintroducing a swirling mass of air into the upstream end portion of saidswirl chamber 66 and then into the upstream end of said flame tube 12.As illustrated in FIGS. 9 and 10, said air inlet means comprises aplurality of air conduits 68 extending into said swirl chamber 66tangentially with respect to the inner wall thereof. Said conduitsextend from annular space 74, similarly as in FIG. 1. The fuel inletmeans in the combustor of FIG. 9 comprises a fuel supply conduit 70which is in communication with three fuel passageways 72, whichcommunicate with annular passageway 74, which in turn is incommunication with a plurality of fuel conduits 76 extendingtangentially through the downstream end portion of said closure member64 and into a recess 78 formed in the downstream end portion of saidclosure member, and tangentially with respect to the inner wall of saidrecess. As illustrated in FIGS. 9 and 10, said air inlet conduits 68 areadapted to introduce air tangentially into swirl chamber 66 in a clockwise direction (when looking downstream), and said fuel inlet conduits76 in FIG. 11 are adapted to introduce fuel tangentially into saidrecess 78 in a counterclockwise direction. This is a presently preferredarrangement in one embodiment of the invention. However, it is withinthe scope of the invention to reverse the directions of said air inletconduits 68 and said fuel inlet conduits 76, or to have the directionsof both said air inlet conduits and said fuel inlet conduits the same,e.g., both clockwise or both counterclockwise.

Referring now to FIG. 12, there is illustrated another type of closuremember or dome which can be employed with the flame tubes of thecombustors described herein. In FIG. 12 closure member 78 is similar toclosure member 64 of FIG. 9. The principal difference is that in closuremember 78 a conduit means 80 is provided and extends through saidclosure member 78 into communication with the upstream end portion offlame tube 12, for example. At least one swirl vane 82 is positioned insaid conduit means 80 for imparting a swirling motion to the air passingthrough said conduit means 80. If desired, conduit means 80 can comprisean annular conduit, instead of the tubular conduit shown, with suitableswirl vanes installed therein.

FIG. 13 is a diagrammatic illustration of a modification of thecombustor of FIG. 1. In FIG. 13 a plurality of imperforate individualtubular openings 36' are each connected individually to individualopenings 34' in the wall of flame tube 12'. Said tubular conduits 36'extend longitudinally through annular chamber 18' to the upstream endthereof and are provided for admitting a second stream of air into theinterior of said flame tube. Outer casing 16' and dome member 14 areessentially like their counterparts in FIG. 1. A third stream of air isadmitted to the interior of flame tube 12' via said annular chamber 18'and openings 38.

FIG. 14 is a diagrammatic illustration of another modification of thecombustor of FIG. 1, which is similar to the combustor of FIG. 13. Theprincipal difference is that in FIG. 14 the tubular conduits 36 extendtransversely through annular chamber 18' and through outer casing 16 andthen to the upstream end of the combustor.

Referring now to FIG. 15, there is illustrated the upstream portion ofanother combustor in accordance with the invention. The downstreamportion of the combustor of FIG. is like the combustor of FIG. 1. Aclosure member or dome, designated generally by the reference numeral85, is mounted in the upstream end of flame tube 12 so as to close theupstream end of said flame tube except for the openings provided in saidclosure member. Said closure member can be fabricated integrally, i.e.,as one element. However, in most instances it will be preferred tofabricate said closure member in a plurality of pieces, e.g., anupstream element 86, a swirl plate 87 (see FIG. 17), and a downstreamelement or radiation shield 88. An air inlet means is provided forintroducing a swirling mass of air into swirl chamber 89 which is formedbetween swirl plate 87 and radiation shield 88, and then into theupstream end of flame tube 12. As illustrated in FIGS. 15, 16, and 17,said air inlet means comprises a plurality of air conduits 90 and 90extending through said upstream member 86 and said swirl plate 87,respectively. A plurality of angularly disposed baffles 91, one for eachof said air conduits 90, are formed on the downstream side of said swirlplate adjacent the outlets of said air conduits.

A fuel inlet means is provided for introducting a stream of fuel intothe upstream end of flame tube 12. As illustrated in FIG. 15, said fuelinlet means comprises a fuel conduit 92 leading from a source of fuel,communicating with a passageway 93 formed in upstream element 86, whichin turn communicates with chamber 94, also formed in element 86. A spraynozzle 95 is mounted in a suitable opening in the downstream side ofsaid element 86 and is in communication with said chamber 94. Any othersuitable type of spray nozzle and fuel inlet means can be employed,including other air assist atomization nozzles. For example, it iswithin the scope of the invention to employ other nozzle types foratomizing normally liquid fuels such as nozzles wherein a stream of airis passed through the nozzle along with the fuel.

It will be understood the combustors of the invention can be providedwith any suitable type of ignition means and, if desired, means forintroducing a pilot fuel to initiate burning.

In one method of operating the combustor of FIG. 1,

a stream of air from a compressor (not shown) is passed, via a conduitconnected to flange 17, into the upstream end of annular space 18. Afirst stream of air is passed from annular space 18, through tangentialconduits 24, and into swirl chamber 22. Said tangential conduits imparta helical or swirling motion to the air entering said swirl chamber andexiting therefrom. This swirling motion creates a strong vortex actionresulting in a reverse circulation of hot gases within flame tube 12.Said first stream of air comprises and can be referred to as primaryair.

A stream of fuel, preferably prevaporized, is admitted, via conduit 26,axially of said swirling stream of air. Controlled mixing of said fueland said air occurs at the interface therebetween. The fuel and air exitfrom swirl chamber 22 via expansion passageway 28 wherein they areexpanded in a uniform and graduated manner, during at least a portion ofthe mixing'thereof, from the volume in the region of the initial contacttherebetween to the volume of the primary combustion zone, i.e., theupstream portion of flame tube 12.

A second stream of air, separate from said first stream of air, ispassed from the upstream end of annular chamber 18 via second annularchamber 19, tubular conduits 36, and openings 34 into a secons zone ofthe combustor which is located downstream from said primary combustionzone. Said second stream of air comprises and can be referred to assecondary air.

A third stream of air, separate from said first and second streams ofair, is passed from the upstream end of annular chamber 18, via theenclosed portion 18, around tubular conduit 36, into the downstreamportion of annular chamber 18, and then via openings 38 into a thirdzone of the combustor which is located donwstream from said second zone.Said third stream of air comprises and can be referred to as quench air.

In the above method of operation, combustion of said fuel is initiatedat least in said primary combustion zone with said first stream of air(primary air) and essentially completed, if necessary, in said secondzone with said second stream of air. The resulting combustion gases arequenched in said third zone and the quenched gases exit the downstreamend of the flame tube to a turbine or other utilization such as afurnace, boiler, etc. In the above method of operation, said thirdstream of air in flowing through enclosed portion 18 removes heat fromthe wall of the primary combustion zone thus lowering its temperature,thereby increasing the heat loss from the combustion gases, and therebylowering the flame temperature within the primary combustion zone.Preferably, the outer wall of the primary combustion zone is providedwith an extended surface, e.g., fins as shown in FIG. 1, so as toincrease said heat removal from the primary combustion zone. A furtheradvantage is realized in that said second stream of air flowing throughannular chamber 19 is shielded from the hot wall of the combustor and isrelatively cool. This also aids in reducing the flame temperature in theprimary combustion zone. The air which is heated by heat loss from thecombustor wall is used only in the quench zone of the combustor. This isa further aid in reducing said flame temperature by keeping said heatedair out of the primary combustion zone; but the overall efficiency ismaintained by the introduction of the heated air into said quench zone.As shown by the examples hereinafter, outstanding results. have beenobtained in reducing the emissions content of the combustor gases,particularly with respect to decreasing the nitrogen oxides emissions.

In the above method of operationthe relative volumes of said first,second, and third streams of air can be controlled by varying the sizesof the said openings, relative to each other, through which said streamsof air are admitted to flame tube 12. Any other suitable method ofcontrolling said air volumes can be employed. For example, flow metersor calibrated orifices can be employed in the conduits supplying saidstreams of air.

In one method of operating the combustor of FIG. 7, a stream of air froma compressor (not shown) is passed, via a conduit connected to flange17, into annular space 18. A first stream of air is passed from annularspace 18 through tangential conduits 54 into swirl chamber 52. SAidtangential conduits 54 impart a helical or swirling motion to the airentering said swirl chamber and exiting therefrom. This swirling motioncreates a strong vortex action resulting in a reverse circulation of hotgases within flame tube 12 upstream toward said swirl chamber 52 duringoperation of the combustor.

A stream of fuel, preferably prevaporized, is adm te ,X a s me? p ssa a58, a fuel passageway 60. Fuel exiting from fuel passageway 60 is formedinto an annular stratum around the swirling stream of air exiting fromswirl chamber 52. This method of introducing fuel and air effects acontrolled mixing of said fuel and air at the interface therebetween.Initial contact of said fuel and air occurs upon the exit of said airfrom said swirl chamber 52. Immediately after said initial contact thefuel and air streams (partially mixed at said interface) are expanded,in a uniform and graduated manner during passage of said fuel and airthrough the flared portion of member 50, from the volume thereof in theregion of said initial contact to the volume of said combustion chamberand at a point in said flame tube downstream from said initial contact.Said expansion of fuel and air thus takes place during at least aportion of the mixing of said fuel and said air. The resulting mixtureof fuel and air is burned and combustion gases exit the downstream endof flame tube 12. A second stream of air is admitted to the interior offlame tube 12 from the upstream end of annular chamber 18 via secondannular chamber 19, tubular conduits 36, and openings 34 as describedabove in connection with FIG. 1. A third stream of air is admitted tothe interior of flame tube 12 via openings 38 as described above inconnection with FIG. 1.

In one presently preferred method of operating the combustor of FIG. 9,the method of operation is similar to that described above for thecombustors of FIGS. 1 and 7. A first stream of air is admitted to swirlchamber 66 via tangential inlet conduits 68 which impart a helical orswirling motion to said air. A stream of fuel, preferably prevaporized,is admitted via conduit 70, fuel passageways 72, and tangential fuelconduits 76 into recess 78 formed at the downstream end of said closuremember 64. Said fuel isthus formed into an annular stratum around theswirling stream of air exiting from swirl chamber 66. This method ofintroducing fuel and air effects controlled mixing of said fuel and airat the interface therebetween. Second and third streams of air areadmitted to the interior of flame tube 12 in the manner described abovein connection with the combustors of FIGS. 1 and 7.

The method of operation of the combustors of FIGS. 13 and 14 can besubstantially like that described above for the combustors of FIGS. 1,7, and 9, taking into consideration the type of dome or closure memberemployed on the upstream end of flame tubes 12. In the combustors ofFIGS. 13 and 14 the second stream of air is admitted to flame tube 12via tubular conduits 36. The third stream of air is admitted viaopenings 38'. In FIG. 14 said tubular conduits 36 can be connected to acommon source of air (such as a header conduit) which also supplies thefirst and third streams of air, or said tubular conduits can beconnected to a separate source of air. The combustor of FIG. 14 isparticularly adapted to be employed in those embodiments of theinvention wherein the stream of secondary air admitted through openings34 can have a temperature greater than the temperature of the primaryair admitted through dome or closure member 14. When tubular conduits36' are connected to the same source of air as in supplying chamber 18the temperature of the secondary air can be substantially the same as,or can be increased to be greater than, the temperature of the primaryair. Similarly, when conduits 36 are connected to a source of air otherthan that supplying chamber 18, the temperature of the secondary air canbe substantially the same as, or greater than, the temperature of theprimary air. Any suitable means can be employed for heating saidsecondary air, e.g., a separate heater or heat exchange means forheating the air passing through said conduits 36'.

In one preferred method, the operation of the combustor of FIG. 15 issimilar to the above-described operation of the combustor of FIG. 1, andreference is made thereto. The principal difference is in the operationof closure member (FIG. 15) and closure member 14 (FIG. 1). In FIG. 15,primary air is passed through said openings and 90', strikes saidbaffles 91, and has a swirling motion imparted thereto in chamber 89. Aswirling stream of air exits from swirl chamber 89 through the openingin radiation shield 88 which surrounds nozzle 95. A stream of liquidfuel is passed through conduit 92, passageway 93, chamber 94, and exitsfrom nozzle in a generally coneshaped discharge. Said fuel contacts saidstream of air, with said air stream assisting the action of nozzle 95 inatomizing'said fuel.

The combustors of the invention wherein heat is removed from thecombustion zone and reintroduced into the quench zone are particularlyadapted to use fuelshigh in aromatic content. This is completely contrato conventional practice. The ASTM specification for Aviation TurbineFuels (D 1655) limits the concentration of aromatics in both Jet A andJet B turbine fuel to 20 percent maximum. Such fules will have ahydrogen content in the range of about 13.5 to 14 weight percent. Onereason for this limitation is to reduce flame radiance and loss of heatto the walls of the combustor. However, in the combustors of theinvention this problem is solved by the above-described method ofintroducing three separate streams of air to the combustor. Thus, theuse of high aromatic content fuels having high flame radiance isdesirable and advantageous in the method of the invention in thatnitrogen oxides emissions can be further reduced. Such fuel will have ahydrogen content of less than about l3.5 weight percent, preferably lessthan about 12 weight percent.

The following examples will serve to further illustrate the invention.

EXAMPLE I A series of test runs was made employing combustors inaccordance with the invention and a typical standard" or prior artcombustor as a control combustor. The same fuel was used in all of saidtest runs. Properties of said fuel are set forth in Table I below.Design details of the combustors of the invention are set forth in TableII below. Said design details, e.g., dimensions, are given by way ofillustration only and are not to be construed as limiting on theinvention. Said dimensions can be varied within wide limits so long asthe improved results of the invention are obtained. For example, theformation of nitrogen oxides in a combustion zone is an equilibriumreaction. Thus, in designing a combustion zone, attention should begiven to the size thereof so as to avoid unduly increasing the residencetime therein. It is desirable that said residence time not be longenough to permit the reactions involved in the formation of nitrogenoxides to attain equilibrium. In said Table II the combustors have beenidentified by a number whichis the same as the FIGURE number of thedrawing in which they are illustrated. Combustor No. l was essentiallyas illustrated in FIG. 1. Combustor No. 1(a) was like combustor No. 1except that the fins on the flame tube were modified by placingone-eighth inch bars longitudinally through each row of fins 40 and eachrow of fins 42. This provided a more linear path through enclosed area18'. Combustor No. 1(b) was like combustor No. 1(a) except that the domeor closure member 14 was modified to use liquid atomized fuel and swirlvanes were employed to impart the helical swirl to the air admittedthrough said dome l4. Combustor No. 7(a) was like the combustorillustrated in FIG. 7 except that the fins on the flame tube weremodified in the same manner as in combustors 1(a) and 1(b).

Said control combustor basically embodies the prin cipal features ofcombustors employed in modern aircraft-turbine engines. It is astraight-through can-type combustor employing fuel atomization by asingle simplex-type nozzle. The combustor liner was fabricated from 2inch pipe, with added internal deflector skirts for air film cooling ofsurfaces exposed to the flame. Exhaust emissions from this combustor,when operated at comparable conditions for combustion, are in generalagreement with measurements presently available from several differentgas turbine engines. Said control combustor had dimensions generallycomparable to the above-described combustors of the invention.

Each of said combustors of the invention and said control combustor wasrun at 12 test points or conditions, i.e., 12 different combinations ofinlet-air temperature, combustor pressure, flow velocity, and heat inputrate. Test points or conditions 1 to 6 simulate idling conditions, andtest points 7 to 12 simulate maximum power conditions. The combustors ofthe invention were run using a prevaporized fuel. The control combustorwas run using an atomized fuel. In all runs the air stream to thecombustors was preheated by conventional means. Analyses for content ofnitrogen oxides (reported as NO), carbon moboxide, and hydrocarbons(reported as carbon) in the combustor exhaust gases were made at eachtest condition for each combustor. Nitrogen oxides were determined bythe Saltzman technique, Anal. Chem. 26, No. 12, 1954, pages 1949-1955.Carbon monoxide was measured by a chromatographic technique. Hydrocarbonwas measured by the technique of Lee and Wimmer, SAE Paper 680679. Eachpollutant measured is reported in terms of pounds per 1,000 pounds offuel fed to the combustor. The results from test conditions 1 to 6 areset forth in Table III BELOW. The results from test conditions 7 to 12are set forth in Table IV below. The data set forth in Tables 111 and IVare mean values from duplicate fruns at each test condition.

TABLE I PHYSICAL AND CHEMICAL PROPERTIES OF TEST FUEL Philjet A-50 ASTMDistillation, F.

Initial Boiling Point 340 5 vol. evaporated 359 vol. evaporated 362 10vol. evaporated 371 30 vol. evaporated 376 40 vol. evaporated 387 50vol. evaporated 398 60 vol. evaporated 409 70 vol. evaporated, 424 80vol. evaporated 442 5 90 vol. evaporated 461 95 vol. evaporated 474 EndPoint 496 Residue, vol. 0.8 Loss, vol. 0.0 Gravity, degrees API 46.6Density, lb./ga1. 6.615 t 2 Heat of Combustion, net, Btu/lb. 18,670Hydrogen Content, wt. 14.2 Smoke Point, mm 27.2 Sulfur, wt. 0.001 Gum,mg/l00 ml. 0.0 Composition, vol.

Paraffins 52.8 Cycloparaffins 34.5 Olefins 0.1 Aromatics 12.6 Formula(calculated) (C H Stoichiometric Fuel/Air Ratio, lb./lb. 0.0676

TABLE II COMBUSTOR DESIGN Combustor Number:

Variable 1 1(a) 7(a) 1(b) Closure member Air inlet diameter, in. 0.8750.875 0.875 0.625

Inlet type tangent tangent tangent swirl Hole diameter, in. 0.188 0.1880. 0 0.250 Number of holes 6 6 6 6 Total hole area, sq. in. 0.166 0.166r 0.295 0.295 total combustor hole area 3.213 3.213 5.571 5.571 Fuelslot, inc. 0.005 Fuel nozzle type Simplex Spray angle, deg. 45 Fuel tubediameter,

in. 0.250 0.250 Flame tube 1st station (34) Hole diameter, in. 5/16 l"5/16X1 5I16 1 5/16X1 Total number of holes 8 8 8 8 Total hole area, sq.in. 2.500 2.500 2.500 2.500 Total combustor hole area 48.393 48.39347.214 47.214 2nd station (38) Hole diameter, in. 5/16X1 5/16Xl S/16X15/16Xl Total number of holes 8 8 8 8 Total hole area, sq. in. 2.5002.500 2.500 2.500 Total combustor hole area 48.393 48.393 47.214 47.214

Combustor cross-sect. area, sq. in. 3.355 3.355 3.355 3.355

Total combustor hole area, sq. in. 5.166 5.166 5.295 5.295cross-sectional area 153.933 153.933 157.777 157.777

Combustor inside diameter, in. 2.067 2.067 2.067 2.067 Primary zonelength,

in. 7.375 7.375 7.375 7.375 Volume, cu. in. 24.748 24.748 24.748 24.748Combustor length. in. 18.437 18.437 18.437 18.437 olume, cu. in. 61.86761.867 61.867 61.867

Holes are 5/16" diameter at ends; slots are 1" long.

TABLE Vl.Summary of Emission Data From Combustor No. 1

Primary zone Resi- Test dence Equiv- Emissions, lbs.l1000 lbs. fuelcondition time, alence N01 l-lC number msec ratio, (15 (as NO) CO (as C)TABLE VII.Summary of Emission Data For Combustor No. 1(b) Bi 11299 Resi-Emissions, lbs/1000 lbs. fuel dence Equivtime, alence NO, I-IC msecratio, 4; (as NO) CO (as C) TABLE Vll.Summary of Emission Data forCombustor No. 1(b)Continued Primary zone RB i- Emissions,lbs./l000 lbs.fuel Test dence Equivcondition time, alence NO, HC number msec ratio,(as NO) CO (as C) The data in the above Tables V1 and VII show thatdecreasing the temperature of the inlet air to the primary combustionzone decreases the NO, emissions. The temperature of the inlet air tothe second zone of the combustor (inlet at openings 34) was not measuredbut approximated the temperature of the primary air introduced throughairinlet conduits 24. CO emissions decreased with an increase intemperature of the inlet air to the second zone of the combustors. Thus,as discussed further hereinafter, in some embodiments of the invention,it is preferred that the temperature of the secondary air admitted tothe second zone of the combustor be greater than the temperature of theair admitted to the primary combustion zone.

Said data also show that, generally speaking, increasing combustorpressure increases NQ emissions; but increasing reference velocitydecreases NO, emissions. In general NO, emissions decrease withincreasing equivalence ratio in the primary combustion zone (increasingfuel-rich mixture), and tend to plateau at low levels with increase inheat input. Said equivalence ratios were calculated from the percentTotal Combustor Hole Area for the air inlet conduits 24 to the primarycombustion zone. See combustors l and 1(b) in Table II. In general, COemissions tended to peak at intermediate levels of heat input, decreasedwith an increase in combustor pressure, and increased with an increasein reference velocity.

EXAMPLE III Another series of test runs was carried out employingcombustor 1 of Example I and five modifications thereof, i.e.,combustors 1(c), 1(d), 1(e), IQ), and 1(g). Referring to FIGS. 1 and 4,said five modified combustors were essentially like combustor 1 exceptfor the diameter of air inlet conduits 24. Design details of saidcombustors are set forth in Table VIII below. Design details ofcombustor 1 are set forth in Table [1 above. Said design details, e.g.,dimensions, are given by way of illustration only and are not to beconstrued as limiting on the invention. Said dimension can be variedwithin wide limits so long as the improved results of the invention areobtained.

Each of said combustors was run at 12 test points or conditions, i.e.,12 different combinations of inlet-air temperature, combustor pressure,flow velocity, and heat input rate, similarly as in Example I. Saidcombustors were run using the same fuel, prevaporized, as in Examples Iand 11. Operating conditions are set forth in 5 TABLE Vlll.-CombustorDesign Combustor number Variable 1(d) l(e) 1(0 Closure member:

Air inlet diameter, (in.) 0.875 0.875 0.875 0.875 lnlet type TangentTangent Tangent Tangent Hole diameter, (in.). 0.125 0.164 0.211 0.230Number of holes..... -6 6 6 6 Total hole ares, (sq. |n.)....... 0.0740.127 0.210 0.249 Percent total comb. hole area. 1.458 2.477 4.030 4.743

Fuel nozzle'type Spray angle, deg..

Fule tube diameter 0.250 0.250 0.250 0.250

Flame tube:

1st station (34):

Hole diameter, (in.). 5/16 X 1 5/1 X1 5/16 X 1 5/16 X 1 Number ofholes....... 8 8 8 8 Total hole area, (sq. in. 2.500 2.500 2.500 2.500Percent total comb. hole area 49.271 48.761 47.985 47.628 2nd station(38):

Hole diameter, (in.) 5/16 X 1 5/16 X 1 5/16 X 1 5/16 X 1 Number of holes8 8 8 8 Total hole area, (sq. in.) 2.500 2.500 2.500 2.500 Percent totalcomb. hole area 49.271 48.761 47.985 47.628 Comb. cross-sect. area, (sq.in.) 3.355 3.355 3.355 3.355 Total comb. hole area, (sq. in.) 5.0745.127 5.210 5.249 Percent cross-sect. area... 151.119 152.771 155.244156.406 Combustor inside diameter, (in. 2.067 2.067 2.067 2.067 Primaryzone length, (in.) 7.375 7.375 7.375 7.375 Volume, (cu. in.) 24.74824.748 24.748 24.748 Combustor length, (in.). 18.437 18.437 18.43718.437 Volume. (cu. in.) 61.867 61.867 61.867 61.867

TABLE V1l1)- Combustor design- Continued Combustor number Variable 1(g)1(h) 1(i) 1(j) Closure member:

Air inlet diameter, (in.) 0.875 0.875 0.875 0.625 Inlet type TangentTangent Tangent Swirl Hole diameter, (in.)... 0.250 0.188 0.250 0.250Number of holes 6 6 6 6 Total hole area, (sq. in.) 0.295 0.166 0.2950.295 Percent total comb. hole area 5.571 3.213 5.571 5.571

Fuel nozzle type Simplex Spray angle, deg. 45

Fuel tybe diameter.... 0.250 0.250 0.250

Flame tube:

1st station (34):

Hole diameter, (in.) 5/16 X 1 5/16 X 1 5/16 X 1 5/16 X 1 Number of holes8 8 8 8 Total hole area, (sq. in.)...... 2.500 2.500 2.500 2.500 Percenttotal comb. hole are 47.214 49.393 47.214 47.214

2nd station (38):

' Hole diameter, (in.) 5/16 X 1 5/16 X 1 5/16 X 1 5/16 x 1 Number ofholes 8 8 8 8 Total hole area, (sq. in.)... 2.500 2.500 2.500 2.500Percent total comb. hole area. 47.214 48.393 47.214 47.214

Comb. cross-sect. area, (sq. in.).. 3.355 3.355 3.355 3.355

Total comb. hole area. (sq. in). 5.295 5.166 5.295 5.295 Percentcross-sect. area.... 157.777 153.933 157.777 157.777

Combustor inside diameter, (in.) 2.067 2.067 2.067 2.067

Primary zone length, (in.). 7.375 7.375 7.375 7.375 Volume. (cu. in.)...24.748 24.748 24.748 24.748

Combustor length, (in.). 18.437 18.437 18.437 18.437

Volume. (cu. in.)...... 61.867 61.867

sure; and CO emissions increased with an increase in reference velocity.

ple 1(j) was a modification of combustor 1 EXAMPLE IV Another series oftest runs was carried out employing three additional combustors 1(h),1(i), and Combustors 1(h) was essentially like combustor l of Example I.Combustor 1(i) was a modification of combustor l and was essentiallylike combustor 1(g) of Exam and was essentially like combustor 1(b) ofExample I. Design details of said combustors are set forth in TableTABLE IX.-Test Conditions Combustors l. l(c). l(d), [(e), l(0.and 1(a)Com- Cold Primary bustor flow inlet air presrefer Heat tempersure, enceinput, Air Fuel ature, in. Hg. velocity, Btu/lb. flow, flow, F abs.ftJsec. air lb./sec. lb./hr.

---------- 10 III. Combustor Test condition number y, and

1 22 2 2 1 000000 7287 25 J .2 233460 334572 I l I 322222 111112 000000728725 J I 233460 222348 I Each of said combustors was run at 12 testpoints or conditions, i.e., 12 different combinations of inlet air 25.220 temperature, combustor pressure, flow velocit u I I u a a I u I u u2482 N222223l 00O000 4 698 .5J2 S M s 456796 334572 a f a 1 l VIIIabove. Said design details, e.g., dimensions, are

given by way of illustration only and are not to be con- 15 strued aslimiting on the invention. Said dimensions can be varied within widelimits so long as the improved results of the invention are obtained.

heat input rate, similarly as in Example I. Said combustors were runusing the same fuel as in the other examg 1 & O l l o 1 n kw l 1, a S..D r m lu m u 922222 1 f000000 4 698 JA .6 S n 0 456796 222348 B b 0 S6 m m I w w m I ll wmm Ham Hnu HM o n 6 m .s .s 2o2 .jsiflszm I11 I I vC m 2 2C WOOOOOOe7287 5m983629 m 0 H 1 m233460 4568 8 E c I s l n 1e 11r t O b C C M F a 1 H e 5 444 555 555 222 w m T 888 555 444 7772 a S 22244 4 555 8 80 M D m 000 000 000 000 W n S W m 4 m 050 O O50 050 n .m m075 075 520 520 m m 223 223 23 23 2 E M f o 3 v. t 000 000 000 000 M 555000 555 000 m 222 444 222 444 r m v u w s 2 H mmm mmm www wmm m X 111111 E L I .2 B A 000 000 000 000 000 000 000 000 E T 999 999 III 111 IIIIII m w T m m I S H M UH n 2 b n mm H n u u 23 456 WHU Cn The data inthe above Table X show that practially ples. Combustors 1(h) and- 1(i)were run using prevaporized fuel. Combustor 10') was run using atomizedliquid fuel. Operating conditions were the same as for the runs inExample III and are set forth in Table IX above. Analyses of thecombustor exhaust were carried combustor pressure. and the referencevelocity at fixed out as in the other examples. Emission data, meanvalues from duplicate runs at each test condition, are set forth inTable XI below.

all NO emission values obtained were good low values for the runs thereset forth. Said data also show, in general, that: CO emissions decreasewith an increase in heat input when holding the inlet air temperature,the

values; CO emissions decreased with an increase in inlet air temperatureand increase in combustor pres- TA BLF. Xl.- Summary of Emission DataCombustors 1(h), l(i),und 1(j) Emissions. lbs/1000 lbs. fuel forcombustor confg. Nos.

NO, (as NO) CO HC (as C) Test :on- Combustor No. Combustor No. CombustorNo.

ition Number 1(h) 1(i) 1 3 1(h) 1(i) 1 3 1(h) 1(i) Hi) 7 3.2 Lo 24,1 3550 2 9 2 0,6 0.4 8 2.9 1.8 2.0 6 10 7 0.2 0.2 0.2 t 9... 2.4 1.8 2.0 2 40.1 0.2 0.1

in general, the data in Table X1 confirm the data set forth in Table Xabove.

In the above examples, the fuel to the combustors of the invention,except for combustor Nos. 1(b) and IQ), was prevaporized. The inventionis clearly not limited to using prevaporized fuels and it is within thescope of the invention to employ atomized liquid fuels. For comparisonpurposes, all the runs set forth in the above examples were carriedout'under the conditions of inlet air temperature, combustor pressure,flow velocity, and heat input rate set forth in Tables 111, V and 1X.The invention is not limited to the values there given for saidvariables. It is within the scope of the invention to operate thecombustors of the invention under any conditions which give the improvedresults of the invention. For example, it is within the scope of theinvention to operate said combustors at inlet air temperatures withinthe range of from ambient temperatures or lower to about l,500 F. orhigher; at combustor pressures within the range of from about 1 to about40 atmospheres or higher; at flow velocities within the range of fromabout 1 to about 500 ft. per second or higher; and at heat input rateswithin the range of from about 30 to about 1,200 Btu per pound, of air.Generally speaking, operating conditions in the combustors of theinvention will depend upon where the combustor is employed. For example,when the combustor is employed with a high pressure turbine, higherpressures and higher inlet air temperatures will be employed in thecombustor. Thus, the invention is not limited to any particularoperating conditions. In one preferred method of operating thecombustors of the invention, the above-referred-to first and secondstream of air will be relatively cool (compared to the third stream ofair), and can be at substantially the same temperature. Said thirdstream of air preferably will be heated to a temperature within therange of 100 to 500 F. greater than the temperature of said first andsecond streams of air, in many instances.

in another preferred method of operating the combustors of theinvention, the temperature of the abovereferred-to second stream of aircan be from about 100 to about 500 F. greater than said first stream ofair. In this embodiment of the invention, said third stream of air can,if desired for best results, have a temperature from about 100 to about500 F. greater than the temperature of said first stream of air orsecond streamof air.

The relative volumes of the above-described first, second, and thirdstreams of air will depend upon the other operating conditions.Generally speaking, the combined volume of saidfirst stream of aircomprising primary air and said second stream of air comprisingsecondary air will be a minor proportion of the total air to thecombustor, e.g., less than about 50 volume percent, with said firststream of air being in the range of up to about 25 volume percent andsaid second stream of air being in the range of up to about 24 volumepercent. The volume of said third stream of air comprising quench airwill be a major portion of the total air to the combustor, e.g., morethan about 50 volume percent.

The data set forth in the above Tables 111, IV, VI, VII, X, and XI showthat combustors can be operated in accordance with the invention to givelow N0 low CO, and low HC emissions when using either a prevaporizedfuel or an atomized liquid fuel. Said data also show that the variousoperating variables or parameters are interrelated. Thus, a change inone variable or parameter may make it desirable to adjust one or more ofthe other operating variables or parameters in order to ob taindesirable results with respect to all three pollutants N0 CO, and HC(hydrocarbons).

in one presently preferred method of the invention, the primarycombustion zone is preferably operated fuel-rich with respect to theprimary air admitted thereto. Thus, the equivalence ratio in the primarycombustion zone is preferably greater than stoichiometric. In thismethod of operation, the second zone (secondary combustion zone) of thecombustor is preferably operated fuel-lean with respect to any unburnedfuel and air entering said second zone from said primary zone, and anyadditional air admitted to said second zone. Thus, the equivalence ratioin said second zone preferably is less than stoichiometric. This methodof operation is preferred when it is desired to obtain both low NO, andlow CO emissions from a combustor. In general, it is preferred that thetransition from the fuel-rich condition in the primary combustion zoneto the fuel-lean condition in the secondary zone be sharp or rapid,e.g., be effected as quickly as possible. While it is presentlypreferred that the primary combustion zone be operated fuel-rich asdescribed, it is within the scope of the invention to operatethe primarycombustion zone fuel-lean. Thus, it is within the scope of the inventionto operate the primary combustion zone with any equivalence ratio whichwill give the improved results of the invention.

For example, in the practice of the invention as carried out in lowcompression ratio combustors, e.g., compression ratios up to about 5,the equivalence ratio in the primary combustion zone can have any valuesuch that the NO emissions value in the exhaust gases from the combustoris not greater than about 5 pounds, preferably not greater than about3.5 pounds, per 1,000 pounds of fuel burned in said combustor.Preferably, said equivalence ratio will be at least 1.5, more preferablyat least 3.5, depending upon the other operating variables orparameters, e.g., temperature of the inlet air to the primary combustionzone.

It will be understood that said NO emission values referred to in thepreceding paragraph can be greater than the valves there given whenoperating high performance combustors. For example, combustors such asthe intermediate compression ratio combustors having a compression ratioof about to atmospheres and the high compression ratio combustors havinga compression ratio of about 15 to about 40 atmospheres used in jetaircraft and other high performance engines. The NO, emissions from suchhigh performance or high compression ratio combustors will naturally behigher than the NO,, emissions from low compression ratio combustors.Thus, greatly improved results in reducing NO, emissions from a highperformance combustor can beobtained without necessarily reducing saidNO, emissions to the same levels as would be obtained from a lowperformance combustor.

As used herein and in the claims, unless otherwise specified, the termequivalence ratio for a particular zone is defined as the ratio of thefuel flow (fuel available) to the fuel required for stoichiometriccombustion with the air available. Stated another way, said equivalenceratio is the ratio of the actual fuel-air mixture to the stoichiometricfuel-air mixture. For example, an equivalence ratio of 2 means thefuel-air mixture in the zone is fuel-rich and contains twice as muchfuel as a stoichiometric mixture.

The data in the above examples show that the temperature of the inletair to the primary combustion zone can be an important operatingvariable or parameter in the practice of the invention. As stated above,the invention is not limited to any particular range or value for saidinlet air temperature. It is within the scope of the invention to useany primary air inlet temperature which will give the improved resultsof the invention. For example, from ambient or atmospheric temperaturesor lower to about 1,500 F. or higher. However, considering presentlyavailable practical materials of construction, about l,200 F. to aboutl,500 F. is a practical upper limit for said primary air inlettemperature in most instances. Considering other practical aspects, suchas not having to cool the compressor discharge stream, about 200 to 400F. is a practical lower limit for said primary air inlet temperature inmany instances. However, it is emphasied that primary air inlettemperatures lower than 200 F. can be used, e.g., in low compressionratio combustors.

The data in the above examples also show that the temperature of the airadmitted to the second zone of the combustor (secondary air) can be animportant operating variable or parameter, particularly when the lowerprimary air inlet temperatures are used, and it is desired to obtain lowCO emission values as well as low NO, emission values. Said data showthat both low NO, emission values and low CO emission values can beobtained when the temperature of the inlet air to both the primarycombustion zone and the second zone of the combustor are at least about900 F. As the temperature of the inlet air to said zones decreases,increasingly improved (lower) values for NO, emissions are obtained, butit becomes more difficult to obtain desirably low CO emission values. Insome instances, it is preferred that the temperature of the inlet air tothe primary combustion zone not be greater than about 700 F. Thus, insome embodiments of the invention, it is preferred that the temperatureof the secondary air admitted to .the second zone of the combustor begreater than the temperature of the primary air admitted to the primarycombustion zone. For example, in

. such instances, depending upon the temperature of the inlet air to theprimary combustion zone, it is preferred that the temperature of theinlet air to the secondary zone be in the range of from about to about500 F. greater than the temperature of said inlet primary air. Anysuitable means can be employed for heating said secondary air. Thecombustors illustrated in FIGS. 13 and 14 are well suited forintroducing heated streams of secondary air via tubular conduits 36.

As a further guide to those skilled in the art, but not to be consideredas limiting on the invention, presently preferred operating ranges forother variables or parameters are: heat input, from 30 to 500 Btu perlb. of total air to the combustor; combustor pressure, from 3 to 10atmospheres; and reference air velocity, from 50 to 250 feet per second.

Reference has been made herein to vehicle emission standards which havebeen set by the United States Environmental Protective Agency for1975-1976. These standards or goals have been related to gas turbineengine combustors, by assuming 10.0 miles per gallon fuel economy and6.352 pounds per gallon JP-4 fuel, as follows:

' EMISSION LEVEL CRITERIA Nitrogen oxides 0.9 Carbon monoxideHydrocarbons Particulates 0.40 (as N0 3.4 ll.8 0.41 (as hexane) L2 (ascarbon) 3 0.l

The data set forth in the above examples show that' the invention can bepracticed to give pollutant emission levels meeting the above standardsor goals. How ever, the invention is not limited to meeting saidstandards or goals. Many persons skilled in the art consider saidstandards or goals to be unduly restrictive. It is possible that saidstandards or goals may be relaxed. Thus, a combustor, and/or a method ofoperating a combustor, to obtain reduced levels of pollutant emissionsapproaching said standards or goals has great potential value. While itis not to be considered as limiting on the invention, it is believedthat practical maximums for low compression ratio gas turbine enginegoals would be in the order of, in lbs. per 1,000 lbs. of fuel burned:N0 5; CO, 25; and hydrocarbons, 2.

The term air is employed generically herein and in the claims, forconvenience, to include air and other combustion-supporting gases.

While the invention has been described, in some instances, withparticular reference to combustors employed in combination with gasturbine engines, the invention is not limited thereto. The combustors ofthe invention have utility in other applications, e.g., boilers, otherstationary power plants, etc.

Thus, while certain embodiments of the invention have been described forillustrative purposes, the invention is not limited thereto. Variousother modifications or embodiments of the invention will be apparent tothose skilled in the art in view of this disclosure. Such modificationsor embodiments are within the spirit and scope of the disclosure.

We claim:

1. A method for burning a fuel in a combustor, which method comprises:

establishing separate streams of air as a first stream of air, a secondstream of air, and a third stream of air;

1. A method for burning a fuel in a combustor, which method comprises:establishing separate streams of air as a first stream of air, a secondstream of air, and a third stream of air; introducing said first streamof air into a primary combustion zone of said combustor; introducing afuel into said primary combustion zone; burning said fuel; introducingsaid second stream of air, maintained separate from said first stream ofair, into a secondary combustion zone of said combustor locateddownstream from said primary combustion zone; flowing said third streamof air, maintained separate from said first and second streams of air,in a downstream direction over and in heat exchange with an outer wallof said primary combustion zone so as to remove heat from the interiorof said primary combustion zone and heat said air; and introducing saidthus-heated third stream of air into a third zone of said combustorlocated downstream from said second zone.
 2. A method according to claim1 wherein said first stream of air comprising primary air is not morethan about 25 percent of the total air introduced into said combustor.3. A method according to claim 1 wherein said first streAm of aircomprising primary air is not more than about 5.6 percent of the totalair introduced into said combustor.
 4. A method according to claim 1wherein both said first and said second streams of air are relativelyhot and have a temperature of at least about 900* F.
 5. A methodaccording to claim 1 wherein said fuel has a hydrogen content of lessthan about 13.5 weight percent.
 6. A method according to claim 1wherein: the temperature of the inlet air to said primary combustionzone is not greater than about 1,200* F. to about 1,500* F.; and theequivalence ratio in said primary combustion zone is greater thanstoichiometric and has a value such that the NOx value in the exhaustgases from said combustor is not greater than about 5 pounds per 1,000pounds of fuel burned in said combustor.
 7. A method according to claim6 wherein the CO value in said exhaust gases is not greater than about25 pounds per 1,000 pounds of fuel burned in said combustor.
 8. A methodaccording to claim 6 wherein said equivalence ratio is at least 1.5. 9.A method according to claim 6 wherein said equivalence ratio is at least3.5.
 10. A method for burning a fuel in a combustion zone having aprimary combustion zone, a secondary combustion zone located downstreamfrom said primary combustion zone, and a quench zone located downstreamfrom said secondary combustion zone, which method comprises:establishing separate streams of air as a first stream of air comprisingprimary air, a second stream of air comprising secondary air, and athird stream of air comprising quench air; introducing a stream of fuelinto said primary combustion zone; introducing said first stream of aircomprising primary air into said primary combustion zone in an amountrelative to said fuel sufficient to provide a fuel-rich mixture havingan equivalence ratio in said primary combustion zone greater thanstoichiometric; burning said fuel; introducing said second stream of aircomprising secondary air, maintained separate from said first stream ofair, into said secondary zone, in an amount sufficient to provide afuel-lean mixture in said secondary zone with respect to any unburnedfuel entering said secondary zone from said primary zone, and at atemperature at least 100*F. greater than the temperature of saidintroduced primary air; flowing said third stream of air, maintainedseparate from said first and second streams of air, in a downstreamdirection over and in heat exchange relationship with an outer wall ofsaid primary combustion zone so as to remove heat from the interior ofsaid primary combustion zone and heat said third stream of air; andintroducing said thus-heated third stream of air into said quench zoneat a temperature greater than the temperature of said secondary air. 11.A method for burning a fuel in a combustor, which method comprises:introducing a first stream of air into a primary combustion zone of saidcombustor; introducing a fuel into said primary combustion zone; burningsaid fuel; introducing a second stream of air, separate from said firststream of air, and at a temperature at least 100*F. greater than thetemperature of said first stream of air, into a secondary combustionzone of said combustor located downstream from said primary combustionzone; passing a third stream of air, separate from said first and secondstreams of air, in heat exchange with an outer wall of said primarycombustion zone so as to remove heat from the interior of said primarycombustion zone and heat said air; and introducing said thus-heatedthird stream of air into a third zone of said combustor locateddownstream from said second zone.
 12. A method for burning a fuel in acombustor, which method comprises: introducing a first stream of airinto a primary combustion zone of said combusTor; introducing a fuelinto said primary combustion zone; burning said fuel; introducing asecond stream of air, separate from said first stream of air, and at atemperature within the range of from about 100* to about 500*F. greaterthan the temperature of said first stream of air, into a secondarycombustion zone of said combustor located downstream from said primarycombustion zone; passing a third stream of air, separate from said firstand second streams of air, in heat exchange with an outer wall of saidprimary combustion zone so as to remove heat from the interior of saidprimary combustion zone and heat said air; and introducing saidthus-heated third stream of air into a third zone of said combustorlocated downstream from said second zone.
 13. A method according toclaim 12 wherein the temperature of said first stream of air is notgreater than about 700* F.
 14. A method according to claim 13 whereinthe equivalence ratio in said primary combustion zone is greater thanstoichiometric and has a value such that the NOx emissions value in theexhaust gases from said combustor is not greater than about 5 pounds per1,000 pounds of fuel burned in said combustor.
 15. A method according toclaim 14 wherein the CO emissions value in the exhaust gases from saidcombustor is not greater than about 25 pounds per 1,000 pounds of fuelburned in said combustor.
 16. A method according to claim 15 wherein theequivalence ratio in said primary combustion zone is at least about 3.5.17. A method for burning a fuel in a combustion zone having a primarycombustion zone, a secondary combustion zone located downstream fromsaid primary combustion zone, and a quench zone located downstream fromsaid secondary combustion zone, which method comprises: introducing astream of fuel into said primary combustion zone; introducing a firststream of air comprising primary air into said primary combustion zoneat a temperature not greater than about 700*F. and in an amount relativeto said fuel sufficient to provide a fuel-rich mixture having anequivalence ratio in said primary combustion zone greater thanstoichiometric; burning said fuel; introducing a second stream of aircomprising secondary air, separate from said first stream of air, intosaid secondary zone, in an amount sufficient to provide a fuel-leanmixture in said secondary zone with respect to any unburned fuelentering said secondary zone from said primary zone, and at atemperature within the range of from about 100* to about 500*F. greaterthan the temperature of said introduced primary air; passing a thirdstream of air, separate from said first and second streams of air, inheat exchange relationship with an outer wall of said primary combustionzone so as to remove heat from the interior of said primary combustionzone and heat said third stream of air; and introducing said thus-heatedthird stream of air into said quench zone at a temperature greater thanthe temperature of said secondary air.
 18. A method according to claim17 wherein the exhaust gases from said quench zone have a NOx emissionsvalue not greater than about 5 pounds per 1,000 pounds of said fuelburned, and a CO emissions value not greater than about 25 pounds per1,000 pounds of said fuel burned.
 19. A method for burning a fuel in acombustor, which method comprises: introducing a first stream of airinto a primary combustion zone of said combustor; introducing a fuelinto said primary combustion zone; burning said fuel; introducing asecond stream of air, separate from said first stream of air, into asecondary combustion zone of said combustor located downstream from saidprimary combustion zone; passing a third stream of air, separate fromsaid first and second streams of air, in heat exchange with an outerwall of sAid primary combustion zone so as to remove heat from theinterior of said primary combustion zone and heat said air; andintroducing said thus-heated third stream of air into a third zone ofsaid combustor located downstream from said second zone; and whereinsaid third stream of air is passed in a first annular stream surroundingsaid wall of said primary combustion zone and at least a portion of saidsecond zone, and then introduced into said third zone; and said secondstream of air is passed in a second annular stream surrounding butseparated from said first annular stream, and then introduced into saidsecond zone.